In-process vision detection of flaw and FOD characteristics

ABSTRACT

An inspection system ( 9 ) includes an idler wheel ( 61 ) that is coupled to a fabrication system ( 8 ) and is in contact with a backing layer ( 65 ) of an applied material ( 64 ), A rotation sensor ( 63 ) monitors the idler wheel ( 61 ) and generates a rotational signal. A controller ( 24 ) is coupled to the rotation sensor ( 63 ) and determines a characteristic of one or more flaws and FOD ( 19 ) on a composite structure ( 12 ) in response to the rotation signal.

RELATED APPLICATIONS

This application is a divisional of, and claims priority from, pendingprior application Ser. No. 10/904,727, filed Nov. 24, 2004. Otherrelated applications include U.S. patent application Ser. Nos.09/819,922; 10/846,974; and 10/904,719.

BACKGROUND INFORMATION

1. Technical Field

The present invention relates generally to the fabrication of compositestructures and to material placement machines. More particularly, thepresent invention relates to systems and methods of detecting flaws andforeign object debris (FOD) and characteristics thereof during thefabrication of a composite structure.

2. Background of the Invention

Composite structures have been known in the art for many years. Althoughcomposite structures can be formed in many different manners, oneadvantageous technique for forming composite structures is a fiberplacement or automated collation process. According to conventionalautomated collation techniques, one or more ribbons of compositematerial, known as composite strands or tows, are laid down on asubstrate. The substrate may be a tool or mandrel, but moreconventionally, is formed of one or more underlying layers of compositematerial that have been previously laid down and compacted.

Conventional fiber placement processes in the formation of a partutilize a heat source to assist in the compaction of the plies ofcomposite material at a localized nip point. In particular, the ribbonsor tows of the composite material and the underlying substrate areheated at the nip point to increase resin tack while being subjected tocompressive forces to ensure adhesion to the substrate. To complete thepart, additional strips of composite material can be applied in aside-by-side manner to each layer and can be subjected to localized heatand pressure during the consolidation process.

Unfortunately, defects can occur during the placement of the compositestrips onto the underlying composite structure. Such defects can includetow gaps, overlaps, dropped tows, puckers, and twists. Additionally,foreign objects and debris (FOD), such as resin balls and fuzz balls,can accumulate on a surface of the composite structure. Resin balls aresmall pieces of neat resin that build up on the surfaces of the fiberplacement head as the pre-impregnated tows pass through the guides andcutters. The resin balls become dislodged due to the motion andvibration of the fiber placement machine, and drop on to the surface ofthe ply. Subsequent courses of applied layers cover the resin ball and aresultant bump is created in the laminate whereat there may be nocompaction of the tows. The fuzz balls are formed when fibers at theedges of the tows fray and break off as the tows are passed through thecutter assembly. The broken fibers collect in small clumps that fallonto the laminate and are covered by a subsequent layer.

Composite structures fabricated by automated material placement methodstypically have specific maximum allowable size requirements for eachflaw, with these requirements being established by the productionprogram. Production programs also typically set well-definedaccept/reject criteria for maximum allowable cumulative defectwidth-per-unit-area.

Composite laminates fabricated by fiber placement processes aretypically subjected to a 100% ply-by-ply visual inspection for bothdefects and FOD. Typically, these inspections are performed manuallyduring which time the fiber placement machine is stopped and the processof laying materials halted until the inspection and subsequent repairs,if any, are completed. In the meantime, the fabrication process has beendisadvantageously slowed by the manual inspection process and machinedowntime associated therewith.

Current inspection systems are capable of identifying defects in acomposite structure during the fabrication process without requiringmachine stoppage for manual inspections. The inspection systems arecapable of detecting, measuring, marking, and identifying FOD“in-process” or during the fabrication of a composite structure. This,in turn, eliminates the need for manual FOD inspections and the machinedowntime associated therewith.

It is desirable that an inspection system be capable of determiningcharacteristics of flaws and FOD, including size, location, type,density-per-unit area, and cumulative defect width-per-unit area. Thus,there exists a need for an improved inspection system and method ofdetecting, identifying, and determining characteristics of flaws and FODwithin and during the fabrication of a composite structure.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an inspection systemthat includes an idler wheel. The idler wheel is coupled to afabrication system and is in contact with a backing layer of an appliedmaterial. A rotation sensor monitors the idler wheel and generates arotational signal. A controller is coupled to the rotation sensor anddetermines a characteristic of one or more flaws and FOD on a compositestructure in response to the rotation signal.

The embodiments of the present invention provide several advantages. Onesuch advantage is the provision of a composite structure in-processfabrication inspection technique that accurately determines flaw and FODcharacteristics.

Another advantage provided by an embodiment of the present invention, isthe provision of a composite structure in-process fabrication inspectiontechnique that accurately determines flaw and FOD characteristicswithout actually communicating with a material placement machine toobtain location coordinates.

Yet another advantage provided by an embodiment of the presentinvention, is the provision of a composite structure in-processfabrication inspection technique that determines the density of flawsand FOD per unit area and the width of the flaws and FOD per unit area.

Furthermore, another embodiment of the present invention identifiesareas of a composite structure for further analysis in view ofprocessing parameters, such as placement speed and programmed gapinformation, and flaw and FOD trends. In analyzing processing parametersand flaw and FOD trends one can adjust fabrication processes to preventfuture flaw and FOD occurrences.

Moreover, the present invention allows for the in-process repair of acomposite structure upon detection of a flaw or FOD.

The present invention itself, together with further objects andattendant advantages, will be best understood by reference to thefollowing detailed description, taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side schematic view of a fabrication system incorporating aflaw and FOD inspection system in accordance with an embodiment of thepresent invention;

FIG. 2 is a block diagrammatic and perspective view of the positiondetection system and components of a material placement machine inaccordance with an embodiment of the present invention;

FIG. 3 is a perspective view of an application portion of a fabricationsystem incorporating a flaw and FOD inspection system in accordance withanother embodiment of the present invention;

FIG. 4 is a perspective view of light sources according to theembodiment of FIG. 2;

FIG. 5 is a perspective view of a fabrication system incorporating aflaw and FOD inspection system in accordance with another embodiment ofthe present invention;

FIG. 6 is a logic flow diagram illustrating a method of determining flawand FOD characteristics during the fabrication of a composite structurein accordance with an embodiment of the present invention;

FIG. 7 is a ply layout illustrating course and frame locations inaccordance with an embodiment of the present invention;

FIG. 8 is a top view of a sample irregularly shaped ply in accordancewith an embodiment of the present invention;

FIG. 9 is a front view of a display and user controls illustrating thedetection of flaws and FOD and indication of flaws and FODcharacteristics in accordance with an embodiment of the presentinvention; and

FIG. 10 is a logic flow diagram illustrating a method of fabricating acomposite structure in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

In each of the following Figures, the same reference numerals are usedto refer to the same components. While the present invention isdescribed with respect to systems and methods of detecting flaws andforeign object debris (FOD) and characteristics thereof during thefabrication of a composite structure, the present invention may beadapted for various applications and systems, such as fabrication ofstructures and components, production line applications, or otherapplications and systems known in the art. The present invention may beapplied to both the fabrication of aeronautical and non-aeronauticalsystems and components.

In the following description, various operating parameters andcomponents are described for one constructed embodiment. These specificparameters and components are included as examples and are not meant tobe limiting.

Also, in the following description the term “foreign object debris(FOD)” refers to any resin ball, fuzz ball, impurity, backing paper,backing film, or other foreign or undesirable object contained within oron a composite structure. FOD may refer to one or more of the statedobjects.

In addition, the term “flaw” refers to any defect within a compositestructure or structure under fabrication. A flaw may refer to a tow gap,an overlap of material, a dropped tow, a pucker, a twist or any otherflaw known in the art.

Referring now to FIG. 1, a side schematic view of a fabrication system 8is shown incorporating a flaw and FOD detection and inspection system 9in accordance with an embodiment of the present invention. Thefabrication system 8 includes a lamination system 10, as best seen inFIGS. 2 and 3, that may utilize an automated collation process to form acomposite structure 12, as shown. The inspection system 9 is positionedproximate the composite structure 12 and includes one or moreillumination devices or light sources 13 (only one is shown) and one ormore detectors 14 (only one is shown). The light sources 13 generatelight arrays 16 that are directed at a portion 18 of the compositestructure 12 to reveal flaws and FOD 19 within that portion 18. Theinspection system 9 also includes a flaw and FOD position detectionsystem 20, which determines the position of the flaws and FOD 19. Acontroller 24 is coupled to the detectors 14 and the position detectionsystem 20 and interprets data received therefrom. The collected data maybe used to adjust the operation of the fabrication system 8, theinspection system 9, and the lamination system 10, and to indicate,detect, and allow for the correction of the flaws and FOD 19. Thecontroller 24 may store the received data and/or related information inthe memory or storage device 26. System parameters and operation may beadjusted via the user interface 28.

During the fabrication of the composite structure 12, the compositestructure 12 may be formed of adjacent tows or strips of composite tape(not shown) to form layers 29. The strips include multiple fibers thatare embedded in a resin or other material, which becomes tacky orflowable upon the application of heat. The strips are arranged on a worksurface 30 of a table, mandrel, or tool 32, and compacted with acompaction roller to form the composite structure 12. A compactionroller 34 can be seen in FIG. 2. The automated collation processincludes guiding the composite strips from material creels (not shown)to an automated collation or fiber placement machine, such as a machinemade by Cincinnati Milacron and Ingersoll Milling Machines. Inparticular, the composite strips are guided to a head unit or assembly36, which may be best seen in FIG. 3, and fed under the compactionroller 34. Focused heat energy is then applied to adhere the incomingmaterial and the underlying previously laid material. With thecombination of pressure and heat, the composite strips are consolidatedinto a previous applied layer to form an additional layer on thecomposite structure 12.

An example of an automated collation technique that may be used isdescribed in U.S. Pat. No. 6,799,519 B2, entitled “Composite MaterialCollation Machine and Associated Method for High Rate Collation ofComposite Materials.” The contents of U.S. Pat. No. 6,799,519 B2 areincorporated herein by reference.

Referring now to the inspection system 9, the light sources 13 arepositioned to emit light arrays at the selected portion 18 of thecomposite structure 12. The light sources may be positioned at variousangles as known in the art, depending on the application. Any number oflight sources may be utilized even though a specific number is shown.

The light sources 13 are positioned relative to the composite structure12 via a mounting apparatus 40. The mounting apparatus 40 includes amain shaft 42, a secondary shaft 44, and a locking clamp 46 foradjusting the position of the light sources 13. The mounting apparatus40, in turn, can be attached to the frame 48, to the detectors 14, tothe bracket 50, or to some other object that defines a common positionfor both the light sources 13 and the detectors 14 to maintain aconstant spatial relationship relative to one another.

The light sources 13 may be selected from an infrared light or anothertype of light having an infrared component, such as a halogen lightsource or other incandescent light sources. In other embodiments, thelight sources 13 are in the form of a fluorescent light source (e.g.,white light LEDs, a low pressure/mercury filled phosphor glass tube,etc.), a strobe or stroboscopic light source, a noble gas arc lamp(e.g., xenon arc, etc.), a metal arc lamp (e.g., metal halide, etc.), ora laser (e.g., pulsed laser, solid state laser diode array, infrareddiode laser array, etc.). The light from the light sources 13 may passthrough optical fibers to the point of delivery, an example of which isshown in FIG. 5. The light sources 13 may include LEDs arranged in anarray or cluster formation. In one specific embodiment, the lightsources 13 include twenty-four LEDs mounted in an array upon athree-inch square printed circuit board.

In some embodiments, the light sources 13 are operated at a power levelthat increases the infrared (IR) component of the light arrays, whichaids in the inspection of dark tow material, such as carbon. In thisregard, exemplary power levels in the range of approximately one hundredfifty watts (150 W) and in the wavelength range of about seven hundrednanometers to one thousand nanometers (700 nm-1000 nm) may be used.However, the particular power levels and wavelengths for the lightsources 13 depends at least in part on the speed and sensitivity of thedetectors 14, the speed at which the material is being laid, the lightdelivery losses, and the reflectivity of the material being inspected.

The detectors 14 may be of various types and styles. A wide range ofdetectors may be used including commercially available cameras capableof acquiring black and white images. In one embodiment, the detectors 14are in the form of a television or other type of video camera having animage sensor (not shown) and a lens 13 through which light passes whenthe cameras are in operation. Other types of cameras or image sensorscan also be used, such as an infrared-sensitive camera, a visible lightcamera with infrared-pass filtration, a fiber optic camera, a coaxialcamera, a charge coupled device (CCD), or a complementary metal oxidesensor (CMOS). The detectors 14 may be positioned proximate thecomposite structure 12 on a stand (not shown) or mounted to the frame 48or a similar device. In embodiments of the present invention that do notinclude a reflective surface, the detectors 14 may be positionedapproximately six inches from the top surface 52 of the compositestructure 12, and mounted to the frame 48 by way of the bracket 50 andassociated connectors 54. Also, any number of detectors may be utilized.

The controller 24 may be microprocessor based such as a computer havinga central processing unit, memory (RAM and/or ROM), and associated inputand output buses.

The controller 24 may be a portion of a central main control unit, bedivided into multiple controllers, or be a single stand-alone controlleras shown.

The connectors 54 may be rivets, screws, or the like and used to mountthe detectors 14 to the frame 48 in a stationary position.Alternatively, the connectors 54 may be a hinge-type connector thatpermits the light sources 13, the detectors 14, and associated assemblyto be rotated away from the composite structure 12. This embodiment isadvantageous in situations when there is a desire to access parts of thematerial placement device that are located behind the detectors 14 andassociated assembly, such as during maintenance, cleaning, or the like.

The inspection system 9 may also include filters 56 (only one is shown),which may be utilized in conjunction with the lens 58 for filtering thelight passing therethrough. In one embodiment, the filters 56 aredesigned to filter the light such that the infrared component of or acertain infrared wavelength or range of wavelengths of the light is ableto pass into the detectors 14. Thus, the filters 56 may prevent ambientvisible light from entering the detectors 14 and altering the appearanceof the captured image.

Other methods of filtering light can also be used to achieve the same,or at least used to provide a similar result. For example, the detectors14 may be designed to include a built-in filter of equivalent opticalcharacteristics. In addition, the filter 56 may be located between thelens 58 and the detectors 14. Alternatively, the detectors 14 mayinclude image sensors that are sensitive in the infrared spectrum (i.e.,an infrared-sensitive camera), thus eliminating the need for the filters56.

The inspection system 9 may also include a marking device 60 for markingthe location of the defects and the FOD on the composite structure 12.The marking device 60 may be attached to the frame 48 and be triggeredby the controller 24 or similar device when a flaw or FOD is detected.The marking device 60 may deposit ink, paint, or the like onto thecomposite structure 12 in areas where flaws and FOD have been detected.The markings on the composite structure 12 enable the location of theflaws and FOD to be subsequently and readily identified eitherautomatically or manually. The marking device 60 may also be adapted tomark flaws with different colored ink than that used to mark FOD.Alternatively, other marking or indicating methods can also be used,such as markings utilizing a pump-fed felt-tip marker or a spring-loadedmarking pen, indications via audio or visual alerts, and the like.

Referring now also to FIG. 2, a block diagrammatic and perspective viewof the position detection system 20 and components of a materialplacement machine are shown in accordance with an embodiment of thepresent invention. The position detection system 20 includes a materialcollection device 61, an idler wheel 62, and an idler wheel rotationsensor 63. The composite material 64 having a backing layer 65 isdirected around the compaction roller 34 and adhered to the compositestructure 12. As the composite material 64 reaches the compaction roller34 it is heated and adhered to the composite structure 12. As thecomposite material 64 adheres to the composite structure 12 the backinglayer 65 is pulled from the composite material 64, rolled around thecompaction roller 34, around the return roller 66, over the idler wheel62, and into the material collection device 61. The backing layer 65 maybe in the form of a backing paper, as shown, or may be in some otherform known in the art. The compaction roller 34 and the return roller 66are part of a material placement machine or lamination system 10, theentirety of which is not shown. The lamination system 10 may be separatefrom the inspection system 9 and the position detection system 20.

The material collection device 61 may be in the form of a collectionretainer, as shown, may be in the form of a material collection wheel, atake-up reel, a combination thereof, or may be in some other form knownin the art.

The idler wheel 62 rests against the backing layer 65 and rotates as thebacking layer 65 passes thereon. Motion of the backing layer 65indicates that placement of the composite material 64 is in progress.The idler wheel 62 is free to rotate and may apply little to no pressureon the backing layer 65. The idler wheel 62 is coupled to the laminationsystem 15 and is suspended via an idler arm 67. The idler arm 67 may beposition adjustable and pressure adjustable relative to the backinglayer 65. The idler wheel may be keyed, such that the controller 24 maycapture an image of the composite material 64 as it is applied for apredetermined number of idler wheel revolutions.

The rotation sensor 63 is proximate the idler wheel 62 and is coupled tothe idler arm 67. The rotation sensor 63 monitors the rotation of theidler wheel 62 and generates a rotation signal indicative thereof. Therotation sensor may be in the form of an encoder, an infrared sensor, arotary potentiometer, or other sensor known in the art that is capableof detection rotative position and velocity of the idler wheel 62.

The position detection system 20 may also include a collection roller 68and a second rotation sensor or collection sensor 69. The collectionroller is coupled to the collection device 61. The backing layer 65 ispassed over the collection roller and into the collection device 61. Thesecond rotation sensor 69 is proximate the collection roller 68 anddetects the rotational position and velocity of the collection roller68.

Although a return roller 66 is shown, this is intended as one possibleexample. A material placement machine may include a moveable compactionroller or a stationary show, as known in the art.

Referring now to FIGS. 3 and 4, a perspective view of an applicationportion of a fabrication system 8′ incorporating a flaw and FODinspection system 9′ and a perspective view of light sources 13′ areshown in accordance with another embodiment of the present invention.The inspection system 9′ includes two light sources 13′ (only one isshown) positioned relative to the composite structure 12 and thecompaction roller 34 on either side of a reflective surface 70 and adetector 14′. FIG. 3 illustrates an alternative embodiment of thehinge-type connector 54 that mounts the light sources 13′, the detector14′, the reflective surface 70, and associated head assembly 36 to theframe 48 by way of the bracket 50.

The light sources 13 and 13′ and the detectors 14 and 14′, of FIGS. 1and 3, may be translated or moved relative to a composite structure,such as the composite structure 12. The adjustability and movability ofthe light sources 13 and 13′ and detectors 14 and 14′ providesflexibility in the capture of images of a composite structure. Samplesystems including moveable cameras and light sources are described indetail in previously referred to U.S. patent application Ser. No.10/217,805.

Although the light sources 13′ are shown in the form of four halogenlight bulbs 74, other quantities, types, and styles of illuminationsources may be utilized. A light reflection element 76 is located nearthe light sources 13′. The reflection element 76 includes a series oflight reflecting surfaces 78 that redirect the light towards the desiredarea to be illuminated. This levels the illumination across the topsurface of a composite structure and eliminates, or at leastsubstantially reduces, the areas of intense light (i.e., hotspots)created by the brightest portion of the light source. Hotspots can leadto errors during the processing of images. The light reflection elements78 are particularly advantageous for illuminating the curved/contouredsurfaces of the composite structures because the redirection of thelight permits a larger portion of a composite structure to be evenlyilluminated.

The reflection element 76 is curved around the light sources 13′, suchas in a parabolic shape. The reflection elements 78 are in the form ofcurved steps that are substantially parallel to the light source 13′.The distance between and the curvature of the reflection elements 78 maybe selected for sufficient and even illumination generated from the sumof the two light sources 13′. This enables more consistent illuminationof the composite structure 12, which prevents, or at least reduces, theimage-processing errors due to inconsistent illumination of thecomposite structure 12. Alternatively, the shape and/or surfaceconfiguration of the reflection elements 78 may be modified using othertechniques known in the art to produce consistent illumination andscattering of light.

In an exemplary embodiment, seventeen reflection elements are utilizedand have an overall parabolic shape and a range of widths from about0.125 inches at the outer edge of the reflection elements to about 0.250inches at the center of the reflection elements. The reflection elementsalso have a uniform step height of about 0.116 inches. In otherembodiments, however, the reflection elements 78 may be provided withdifferent numbers of steps having different uniform or varying widthsand different uniform or varying step heights.

Furthermore, the reflection elements 78 may be adjusted in order todirect the light produced by the light sources 13′ and scattered by thereflection elements 78 toward the selected portion of a compositestructure. For example, as shown in FIG. 4, the reflection elements 78are mounted to the mounting apparatus 40 with fasteners 80. Thefasteners 80, when loose, are capable of being slid within slots 82 tocorrespondingly adjust the angle of the reflection elements 78 relativeto a composite structure. Once the reflection elements 78 are positionedappropriately, the fasteners 80 are tightened to secure the reflectionelements 78 in the desired position. Adjustments of the reflectionelements 78 can also be enabled by other methods, such as by electronicmeans that permit remote adjustment of the reflection elements 78.

The detectors 14 are positioned near the composite structure 12 and whenin the form of cameras are positioned to capture images of the selectedilluminated portion, which is typically immediately downstream of thenip point at which a composite tow is joined with the underlyingstructure.

The light sources 13, the detectors 14, the reflective surface 16, andany reflection elements 78, may be mounted on the head unit 23 to allowfor continuous capture of real-time data of the composite structure 12.The real time data may be captured as the head unit 36 is transitionedacross the composite structure 12 and as the composite strips are laiddown or applied.

The bracket 50 may be fastened to the hinge type connector 54 via asuitable fastener, such as a thumbscrew or any other fastener that maybe utilized and inserted through hole 72 and then tightened to securethe assembly in place for operation. The fastener may be loosened orremoved, for example, to rotate the light source and detector assemblyaway from the compaction roller 34 and other parts of the fabricationsystem.

The reflective surface 70 may be positioned near the composite structure12, and angled such that the reflective surface 70 reflects an image ofthe illuminated portion to the detectors 14. In one embodiment, theangle of the reflective surface 70 to the composite structure is aboutsixty-five degrees, but the reflective surface 16 can also be positionedat any appropriate angle in order to reflect images of the illuminatedportion to the detectors 14. The detectors 14 may be positioned to pointtoward the reflective surface 70 in order to capture the close-rangeimages of the illuminated portion from the reflective surface 70. Morethan one reflective surface 70 may also be utilized in furtherembodiments of the present invention in which the reflective surface 70cooperate in order to direct the images of the illuminated portion tothe detectors 14.

The reflective surface 70 may be in various positions relative to aselected portion, such as portion 18. Reflective surface 70 can also beutilized to allow the detectors 14 to be placed in an advantageouspositions, which might otherwise be blocked by portions of thecompaction roller 34 and/or other parts of the fabrication system.

The configuration illustrated in FIG. 3 aids in the capturing of imagesof curved/contoured surfaces of a composite structure since thereflective surface 70 is positioned close to the composite structure. Inaddition, this configuration permits the detectors 14 to be positionedaway from a composite structure, to prevent interference between thedetectors 14 and components of the fabrication system 8′. Further, thereflective surface 70 can also provide a “square on” view of theselected portion being inspected, which, in turn, can improve theability to dimension the two gaps for pass/fail decisions.

Referring now to FIG. 5, a perspective view of a fabrication system 8″incorporating a flaw and FOD inspection system 9″ in accordance withanother embodiment of the present invention is shown. The inspectionsystem 9″ includes lights sources (not shown) that are at a remotelocation. The light sources generate light rays, which are passedthrough linear optical fiber arrays or fiber optic cable 90 to point oftransmission 92 via light emitting heads 94. Light arrays are emittedfrom the fiber optic cable 90 toward the selected portion 18′ of thecomposite structure 12′ to detect flaws and FOD 19′. The use of fiberoptic cables simplifies the number of components mounted on the headassembly.

Referring now to FIGS. 6 and 7, a logic flow diagram illustrating amethod of determining flaw and FOD characteristics during thefabrication of a composite structure and a ply layout illustratingcourse and frame locations are shown in accordance with an embodiment ofthe present invention.

In step 95, strips of the composite material 64 are applied to the tool32 to form the composite structure 12.

In step 96, as the strips are applied, the backing layer 65 is removedfrom the composite material 64 in turn causing the idler wheel 62 torotate.

In step 97, the rotation sensors 63 and 69 generate the rotation signalsthat are indicative of the rotational position and velocity of the idlerwheel 62 and the collection roller 68. The rotational signals are alsoindicative of any cessation in the backing layer, such as when thelamination system 10 or the application position of the compositematerial 64 is laterally transitioned to form another column or course.Cessation of motion indicates that material lay-down for the currentcourse has stopped and that a new course may be started. The rotationalsignals may be compared, averaged, and utilized to accurately determineposition of the lamination system 10. The rotational signals may also beutilized to determine when the backing layer is “bunching up” or notpassing through the fabrication system appropriately.

FIG. 7 illustrates a sample single ply 98 of a rectangular compositestructure 99 with frame rows 100 and courses 101. Seven rows of sixteencourses are shown. Of course, any number of rows and courses may becreated. Also each ply, such as ply 98, may be of various shape, anotherexample of which is shown in FIG. 8. The ply 98 is divided into multipleunit areas 102, each of which corresponding to an image frame. Each unitarea 102 may have a width w greater than the width of the strips (notshown) of the composite material being applied and a height h thatcorresponds to a determined number of revolutions of the idler wheel 62.In one embodiment, the unit area width w is approximately equal to seveninches, the width of the composite material plus a half of an inch foreach side of the material. In another embodiment, the height h isapproximately seven inches corresponding to the circumference of theidler wheel 62. The frame numbers may be sequentially assigned even whenthe course number changes.

In step 104, the portion 18 of concern is selected. The portion 18 mayinclude the entire composite structure under formation or may include adiscrete segment or area of the composite structure. In step 105, thelight sources 13 are activated to illuminate the selected portion 18.The light rays 16, which may be in the form of arrays, are generatedsuch that both the flaws and FOD 19 may be detected simultaneouslywithin the selected portion 18. The light sources may be activatedthroughout the material placement process.

In step 106, detectors, such as detectors 14 and 14′, monitor theportion 18 and generate status signals in response to the reflection ofthe light rays 16 off of the portion 18. The status signals containinformation regarding the existence of flaws and FOD in the portion 18.The detectors 14 and 14′ detect light reflection characteristics of theflaws and FOD.

In step 107, the controller 24 determines one or more flaw and FODcharacteristics in response to the rotation signal and the division ofthe current ply. The characteristics may be determined during theapplication of the composite material 64. The flaw and FODcharacteristics may include size, location, position, type,density-per-unit area, cumulative defect width-per-unit area, and anyother flaw and FOD characteristic known in the art. Width information offlaws and FOD provides gap and density information. Manufacturingspecifications that govern automated material placement have acceptancerequirements for various types of defects. For gaps there is a maximumallowable width for a single gap and a maximum allowable total width forof all of the gaps existing within a defined area. Likewise, for FODthere is a maximum allowable number of occurrences with a defined area.Thus, the detector 14 and/or the controller 24 may track the area thathas been inspected and the number and total width of flaws that havebeen detected.

For example, the controller may determine longitudinal and lateralposition of a flaw or FOD in response to the number of frames capturedin a given row and the number of detected cessations per ply. Thedetector 14 or the controller 24 may store an image after a presetnumber of revolutions of the idler wheel 62. The number of revolutionsremains constant and establishes the image frame height. This along withthe constant width of the material course being placed establishes aconstant rectangle, referred to as a frame. The frames are tracked byassigning a discrete number to each frame.

In step 107 A, the controller 24 generates an image count for each ofthe flaws and FOD to determine a linear distance to each of the flawsand FOD. The image count provides a course measurement of longitudinalposition. In step 107 B, the controller 24 generates a revolution countindicative of the revolutions of the idler wheel 62, which is indicativeof the position of the lamination system and any detected flaws and FODin that position. The revolution count provides a fine measurement oflongitudinal position within an image frame. In step 107 C, thecontroller 24 generates a cessation count for each of the flaws and FOD.In step 107 D, the controller 24 may also generate an applied layer orply count indicative of the number of currently applied plies. In step107 E, the controller 24 determines the position of the flaws and FOD inresponse to the image count, the revolution count, the cessation count,and the ply count.

In step 107 F, the controller 24 determines the flaw areal density. Instep 107 F 1, the controller 24 counts the flaws and FOD in a currentframe to generate a current flaw and FOD frame count. In step 107 F 2,the controller 24 sums the current flaw and FOD frame count with flawsand FOD of two adjacent frames of a previous course to generate aresultant sum. In step 107 F 3, the controller 24 determines flaw arealdensity for the portion in response to the resultant sum. The flaw arealdensity is equal to the resultant sum divided by the area of theportion.

In step 107 G, the controller 24 determines size of the flaws and FOD.In step 107 H, the controller 24 determines cumulative gap width perunit area in response to the portion 18, the frame, or a current set offrames and the size.

In step 108, the detected flaws and FOD 19 as well as the relatedcharacteristics thereof are indicated to a user via a display, such asthat shown with respect to FIG. 9.

In step 109, the flaw and FOD characteristics as detected may be storedin an archival error file within the memory 26, such as in an errorfile. The characteristics may include the ply, course, and frame numberassociated with each flaw and FOD. Also, after a preset number ofrevolutions the detectors 14 or the controller 24 may store images ofthe portion 18 within the memory 26. Since the frame size is constant itis possible to establish the location of a defect on the surface bycounting frames from an initial starting point. The detector 14, thecontroller 24, or other device that has access to the stored informationmay determine approximate location of each flaw and FOD therefromseparate from and without being hard-wired to the fabrication system 8and/or the material placement machine, stated with respect to FIG. 2.

Referring now to FIG. 8, a top view of a sample irregularly shaped ply110 is shown. The length of the courses 111 vary over the ply 110 andthus the image frames, corresponding to unit areas 112, are staggered.When a course ends in an angular cut, the last frame in that course maybe assumed to be fully rectangular in shape for the purpose ofdesignating a unit area. Flaw and FOD characteristics may be determinedin response to the frame stagger. In the example embodiment, the unitareas 112 and thus the frames are in a 50% stagger. Each unit area isbordered by half portions of two adjacent unit areas. The unit areas andthe frames may be oriented at any staggered percentage.

When determining flaw areal density, the number of flaws in any affectedframe (diagonally cut frame) is summed with those in two adjacent framesof a previous course instead of one. Cumulative gap width is determinedby measurement across a designated area in a direction perpendicular tothe direction of material placement on a tool. For summation purposesthe gaps may be assumed or assigned to extend an entire length of theaffected image frames, such that location within a frame of gap locationis unnecessary.

Positions of the flaws and FOD may be determined utilizing informationfrom archived positions and engineering disposition and may be resolvedutilizing known in-process flaw and FOD marking techniques.

Referring now to FIG. 9, a front view of a user display screen 120 anduser controls 122 illustrating the detection of flaws and FOD 124 andindication of flaws and FOD characteristics in accordance with anembodiment of the present invention is shown. Although the operation anduse of the display 120 is primarily described with respect to theembodiment of FIG. 1, it may be easily modified for and applied to otherembodiments of the present invention. The user interface 28 includes thedisplay 120, such as that on a computer monitor, and can also include aninput device, such as a keyboard and mouse (not shown), for permittingan operator to move a cursor about the display 120 and input varioussystem settings and parameters. The display 120 may be touch-sensitivefor permitting the operator to input the desired settings by manuallytouching regions of the display screen.

The interface 28 includes an image window 126 in which an image 128, ofthe composite structure 12, is displayed for viewing by an operator orother user. The image 128 may be in the form of an unprocessed orprocessed camera image. When processed the image 128 or a portionthereof may be binarized. During binarization, all shades of gray abovea predetermined threshold value may be changed to white, while all grayshades below the threshold value may be changed to black to heighten thecontrast of defects and improve the accuracy of defect detection. As analternative or in addition to binarization, rates of light level changein the raw image and color changes in the images may be used to identifythe defects and FOD.

The interface 28 also includes a position window 129, which may displaythe ply number, course number, and frame number of the lamination systemin a current state as is related to a currently viewed image.

The controls 122 allow for various user inputs to the system. Thecontrols 122 may be used to adjust the binarization threshold.Generally, the setting of the binarization threshold involves a tradeoffbetween the sensitivity with which defects are detected and theresolution with which the defects are depicted. In one embodiment, thebinarization threshold is set to about 128, which corresponds to themid-point on the 8-bit digitizing range of 0 to 255. However, otherbinarization threshold values may be employed depending at least in parton the particular application, available lighting, camera settings, andother factors known in the art.

The controls 122 also allow the user to adjust or shift the viewing areawithin the window 126. During operation, the window 126 displaysreal-time moving video images of the illuminated portion of thecomposite structure 12 as the detectors 14 and/or the reflective surface18 are moved relative to the composite structure 12. The controls 122may be such to allow the user to input the maximum allowable dimensionalparameters, the acceptable tolerances, as well as other known parametersfor the flaws and FOD.

In addition to displaying images of the composite structure 12, thedisplay screen 80 may also include a defect table 128, which lists thediscovered flaws and FOD and provides related information thereof, suchas location, size, and the like. The display 120 can further includestatus indicators 130 that notify the user whether a particular imagearea is acceptable or not acceptable based on predefined criteria, suchas the maximum allowable dimensional parameters and tolerances.

Referring now to FIG. 10, a logic flow diagram illustrating a method offabricating a composite structure in accordance with an embodiment ofthe present invention is shown. Although the logic flow diagram of FIG.10 is primarily described with respect to the embodiment of FIG. 1, itmay be easily modified to apply to other embodiments of the presentinvention.

In step 150, the fabrication system 8 applies the strips to form thelayers 29 on the substrate 32 to form the composite structure 12. Instep 152, the inspection system 9 illuminates selected areas of or theentire composite structure 12 during the application of the strips todetect the flaws and FOD 19 as described above with respect to themethod of FIG. 5. Flaws and FOD may be detected continuously throughoutthe material placement process and continuously over selected portionsor the entire composite structure 12.

In step 154, the inspection system 9 distinguishes, identifies, anddetermines characteristics of the flaws and FOD 19 and the locationthereof and generates a composite structure defect signal. Examplesregarding systems and methods for identifying defects in a compositestructure during fabrication thereof are included in U.S. patentapplication Ser. No. 09/819,922, filed on Mar. 28, 2001, entitled“System and Method for Identifying Defects in a Composite Structure” andin U.S. patent application Ser. No. 10/217,805, filed on Aug. 13, 2002,entitled “System for Identifying Defects in a Composite Structure”. Thecontents of U.S. patent application Ser. Nos. 09/819,922 and 10/217,805are incorporated herein by reference as if fully set forth herein.

In step 156, the fabrication system 8 may in response to the compositestructure defect signal alter the operation thereof. The fabricationsystem 8 may cease further application of the strips until one or moreportions of the composite structure 12 are repaired, may alter themanner in which the strips are applied, may adjust parameters of thefabrication system 8 or inspection system 9, or may perform other tasksknown in the art.

At any time upon or after the generation of the status signals and/orthe defect signals the controller 24 may store data or images in thestorage device 26 for future or off-line analysis and/or processing.Future analysis may be based on processing parameters, such as materialplacement speed and programmed gap information, and flaw and FOD trends.

The above-described steps in the methods of FIGS. 5 and 8, are meant tobe illustrative examples, the steps may be performed synchronously,continuously, or in a different order depending upon the application.

The present invention provides systems and methods for the simultaneousdetection of flaws and FOD using a single illumination level. Thepresent invention simplifies the detection of the flaws and FOD andallows for efficient identification and repair thereof.

While the invention has been described in connection with one or moreembodiments, it is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of theprinciples of the invention, numerous modifications may be made to themethods and apparatus described without departing from the spirit andscope of the invention as defined by the appended claims.

1. A method of determining flaw and FOD characteristics comprising: rotating an idler wheel via a backing layer of a composite material; monitoring said idler wheel and generating a rotational signal; and determining at least one characteristic of at least one flaw and FOD on a portion of a composite structure in response to said rotation signal using a controller, wherein the controller stores the at least one characteristic of the at least one flaw and FOD for use in correcting the at least one flaw and FOD.
 2. A method as in claim 1 further comprising: acquiring images via at least one detector, counting images to generate an image count; and determining a linear distance along a composite structure in response to said image count.
 3. The method as in claim 2 further comprising illuminating said composite structure.
 4. The method as in claim 2 further comprising storing said images.
 5. The method of claim 2 further comprising synchronizing said acquiring of images with said rotating of idler wheel.
 6. The method of claim 2 further comprising blocking wavelengths of visible light from entering said at least one detector via at least one filter.
 7. A method as in claim 1 further comprising: counting revolutions of said idler wheel to generate a revolution count; and determining a linear distance along a composite structure in response to said revolution count.
 8. A method as in claim 1 wherein said at least one characteristic comprises at least one of size, location, position, type, density-per-unit area, and cumulative defect width-per-unit area.
 9. A method as in claim 1 further comprising: counting revolutions of said idler wheel to generate a revolution count; counting cessations of said idler wheel to generate a cessation count; and determining position of said at least one flaw and FOD in response to said revolution count and said cessation count.
 10. A method as in claim 9 further comprising: counting applied layers of said composite structure to generate an applied layer count; and determining location of said at least one flaw and FOD in response to said revolution count, said cessation count, and said applied layer count.
 11. A method as in claim 1 further comprising: determining size of said at least one flaw and FOD; and determining flaw area density in response to said portion and said size.
 12. A method as in claim 1 further comprising: counting said at least one flaw and FOD in a current frame and course to generate a current flaw and FOD frame count; summing said current flaw and FOD frame count with flaws and FOD of two adjacent frames of a previous course to generate a resultant sum; and determining flaw areal density for said portion in response to said resultant sum.
 13. A method as in claim 1 further comprising: determining size of said at least one flaw and FOD; and determining cumulative gap width per unit area in response to said portion and said size.
 14. A method as in claim 1 further comprising: dividing said composite structure into a plurality of unit areas; and determining said characteristic in response to said division.
 15. A method as in claim 14 further comprising assigning angular cut frames of said plurality of unit areas a full frame unit area.
 16. A method as in claim 1 further comprising altering operation of a fabrication system in response to said at least one characteristic.
 17. A method as in claim 1 wherein determining at least one characteristic comprises determining cumulative gap width through summation of a plurality of gaps laterally across said portion perpendicular to a direction of material placement.
 18. A method as in claim 17 wherein summing said plurality of gaps comprises assigning gap lengths to extend approximately an entire frame length.
 19. A method as in claim 1 further comprising: staggering frames; and determining said at least one characteristic in response to said frame stagger.
 20. The method of claim 1 further comprising using data stored by the controller to adjust operation of at least one of a fabrication system, an inspection system, and a lamination system to correct the at least one characteristic of the at least one flaw and FOD. 